System and method for hierarchical synchronization of a dataset of image tiles

ABSTRACT

A system and method for hierarchical synchronization of tiles between a first dataset and a second dataset by computing and storing multiple composite cluster hash values for multiple clusters in the first and second dataset. For each of the composite cluster hash values, comparing a composite cluster hash value of a particular cluster in the first dataset with a composite cluster hash value of a corresponding cluster in the second dataset. When the composite cluster hash values of the corresponding clusters do not match, retrieving all tile hashes corresponding to all the tiles from the non-matching cluster in the first dataset, and retrieving all tile hashes corresponding to all the tiles from the non-matching cluster in the second dataset. Finally, determining the one or more changed tiles between the non-matching cluster in the first dataset and the non-matching cluster in the second dataset by comparing the corresponding tile hashes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/099,487, filed on Dec. 6, 2013, which is a continuation of U.S. patent application Ser. No. 13/544,599, filed on Jul. 9, 2012, which claims priority to U.S. Provisional Patent Application No. 61/551,112 filed on Oct. 25, 2011, under 35 USC 119(e). The entire disclosures of all applications are incorporated herein by reference.

BACKGROUND

Systems and methods disclosed herein relate generally to tile-based mapping systems. The first web-based mapping systems offered rudimentary mapping applications through a web browser. A first type of system allowed simple map movements by requiring a user to click on navigation arrow buttons surrounding the map view. When a user clicked on an arrow, the map moved a predetermined amount in the direction clicked. There were also buttons for zooming in and out. Other map applications allowed users to drag and draw boxes on the map to relocate the map view. These applications had several disadvantages, including slow rendering and downloading of map views, because the map view was often represented by a single large image file. Each time the map was moved to the left or right, the entire image was re-rendered and re-sent to the client even though only a portion of the image was new. However, the interfaces were well suited to early web browsers, the map interface could be written entirely in HTML or with minimal JavaScript, and since all 0 were fixed, map servers could cache rendered maps. A second type of system adopted a map view and navigation style similar to desktop GIS systems which used browser plug-in technology and development platforms like Java or Flash.

GOOGLE MAPS® introduced the “slippy map” interface that allows users to move and zoom the map, and was written in HTML and JavaScript. A key technology behind the “slippy map” interface was the concept of tile-based mapping. Mapping applications were made responsive by using background maps that had been broken into smaller tiled images. Those tiles were stored, already rendered, on a central server. Because they were already rendered, they could be sent to clients quickly. The tiles were discretely addressed so they could be cached by internet caching services and by clients' own browsers. The map images were broken into smaller pieces so that when users navigated the map view, only the new parts of the map had to be resent from the server.

Tile-based mapping systems are based on multiple discrete zoom levels, each corresponding to a fixed map scale. In tile-based mapping systems, multiple image tiles are used to virtualize a single map view, and image tiles are accessible using a discrete addressing scheme. Also, in tile-based mapping systems, tiled images stored on a server system are sent to a client system with minimal processing, i.e. as much processing is done ahead of time as possible. Optionally, although not required in tile-based mapping systems, tile addressing can follow a single global projection, tiles can be distributed using a client/server system architecture, and tiles can be organized into relatively few, fixed layers. Tile images can be of any size, and can vary from map scale to map scale, or can vary across the same scale or be random in size. What is needed is a system to determine which size is most efficient for a specific purpose.

Referring now to FIG. 1A (PRIOR ART), tiled image sets are created from collections of random source images that may have sizes and boundaries that follow no specific system. Collections of source images can take a variety of forms, for example, high resolution aerial imagery of the fifty largest cities, each represented by a small number (for example 5-50) of large source images (for example 10,000×10,000 pixels). Each of the source images can be a different size, cover a different portion of the earth, or have a different map resolution. Taken together, all the source images for all the cities form a single map layer. Each layer 12 of tile images has multiple scales or levels 14. Every tile set starts with a base scale 221 which is the scale with the highest number and highest resolution imagery. Each subsequent scale is a lower version of the scale preceding it. In the tile creation process, base scale 221 (the highest resolution scale) can be completed before lower resolution scales. Scales 14 include tiles 18 that are addressable by columns 423. Referring now to FIG. 1B (PRIOR ART), exemplary base scale (level 3) 28 is the highest resolution scale in the exemplary series including level one 24 and level two 26, the lowest resolution level (scale) in the series. What is needed is a multi-processor, memory efficient system to create tiled images from source images.

Tiled images are divided into scales, and each scale is divided into rows and columns. The general problem of tile storage is to link a tile's address (layer, scale, row, and column) to a binary block of data. Tiled images can be stored in computer files on a computer-readable medium in a separate file for each tiled image, bundled together into larger files, or database tables. Storing many hundreds or thousands of tiled images in a single file can provide efficiencies that may not be available for other storage means. If the tiled images are written sequentially to a file, retrieval of individual images can be problematic without a way of knowing which the address corresponds to which tiled image. Tile addresses can be stored with each image in the file, but in order to access a specific tiled image, the whole file is scanned, which could be inefficient. What is needed is a system for organizing blocks of data into scales, rows, and columns so that tiled images can be efficiently written to and read from a computer-readable medium.

SUMMARY

The system and method of the present embodiment address the needs of determining which tile size is most efficient for a specific purpose, providing a multi-processor, memory efficient system to create tiled images, and providing a data organization scheme so that tiled images can be efficiently written to and read from a computer-readable medium.

A first method of the present embodiment for determining the tile size for a particular virtualized map view can include, but is not limited to including, the steps of generating a plurality of random map views for a randomly-selected scale, calculating a number of tiles needed to fill each of the random map views for a plurality of tile sizes, calculating a total number of tiles accessed, and a total number of bytes accessed based on the total number of tiles accessed, to fill each of the random map views for the plurality of tile sizes, and selecting an optimum tile size based on minimizing the total number of bytes accessed for the tile size. The step of selecting an optimum tile size can include, but is not limited to including, the step of minimizing a decompression time based on an image format associated with the each of the random map views.

A second method of the present embodiment for converting source image data to tile data can include, but is not limited to including, the steps of (a) selecting at least one source image set, (b) computing a scaling value for the at least one source image set, (c) selecting a base scale for a tile set to be created based on the scaling value, (d) establishing the tile set geographic bounds of the tile set, (e) converting the tile set geographic bounds, (f) for each source image from each of the at least one source image sets (i) determining source image geographic bounds of the source image, (ii) if there is an intersection between the source image geographic bounds and the tile set geographic bounds, (1) loading the source image from a LRU cache, if possible, (2) if the source image is not in the LRU cache, loading the source image into the LRU cache, (3) extracting image data from the source image at the intersection, (4) scaling the image data based on the base scale, (5) storing the scaled image data to a tile storage mechanism, (f) clearing the LRU cache, and (g) repeating steps (a) through (f) for each of the at least one source image sets.

A third method of the present embodiment for storing a dataset of image tiles can include, but is not limited to including, the steps of (a) determining a number of zoom levels, (b) accessing a plurality of cluster files including two top cluster files, the two top cluster files including a first subset of the zoom levels, (c) accessing the image tiles, each of the image tiles having a tile zoom level and a tile location, (d) for each of the image tiles, computing a cluster name based on the tile zoom level and the location, (e) for each of the image tiles, if a selected cluster file from the plurality of cluster files has a name that matches the computed cluster name, (i) computing an image tile pointer for the image tile associated with the computed cluster name, (ii) storing the image tile pointer in a fixed length index in the selected cluster file, and (iii) storing the image tile associated with the computed cluster name in the selected cluster file according to the image tile pointer, and (f) for each of the image tiles, if a selected cluster file from the plurality of cluster files has a name that does not match the computed cluster name, (i) determining an other subset of the zoom levels, the other subset not including the zoom levels of the first subset, (ii) creating a new cluster file as part of the plurality of cluster files, the new cluster file having a new cluster file index of fixed length, the fixed length based on the other subset of zoom levels, the new cluster file associated with the tile location, (iii) computing an image tile pointer for the image tile associated with the computed cluster name based on the tile zoom level and the tile location, (iv) storing the image tile pointer in the new cluster file index in the new cluster file, and (v) storing the image tile associated with the computed cluster name in the new cluster file according to the image tile pointer.

A fourth method of the present embodiment for storing and retrieving tiled image data can include, but is not limited to including, the steps of for each of a plurality of tiles at a pre-selected zoom level from the tiled image data, storing a tile record in a tiled image file, the tile record being associated with a row and a column, creating a lookup table having a direct-lookup value for the tiled record at the row and the column associated with the tiled image, when there are none of the tile records at the row and the column of the lookup table, storing a null value in the lookup table at the row and the column, when there are none of the tile records in a lookup table row in the lookup table, omit the lookup table row from the lookup table, creating a row index file having a null value for each of the omitted lookup table rows, and retrieving an address for a specific tile by executing the steps including, but not limited to seeking to a row position of the row associated with the tile record in the row index file, reading a row index value at the position, positioning the tile index file according to the row index value if the value is non-null, seeking to a column position for the column associated with the tile record, reading an address associated with the tile record, and retrieving the tile record at the address.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A PRIOR ART is a hierarchical block diagram of layers, scales, columns, and tiles;

FIG. 1B PRIOR ART is a pictorial diagram of three zoom levels;

FIG. 2 is a pictorial diagram of the earth mapped to a two-dimensional surface, and with a grid overlain upon the surface;

FIG. 3A is a pictorial diagram of a geodetic projection overlain with a tile scheme;

FIG. 3B illustrates equations that relate a tile address to a geographic bounding rectangle;

FIG. 4A illustrates an equation to compute dots per pixel;

FIG. 4B is a table relating zoom levels to a number of tiles and dots per pixel;

FIG. 5 is a schematic diagram of a virtualized map view and wasted pixels;

FIG. 6 is a table relating image size to format overhead;

FIG. 7A is a schematic block diagram of the system of the present embodiment for determining tile size;

FIG. 7B is a flowchart of the method of the present embodiment for determining tile size;

FIG. 8A is a software code listing for a random map center algorithm;

FIG. 8B is a software code listing for a random map view generator algorithm;

FIG. 9A is a table relating tile size to wasted pixels;

FIG. 9B is a graph of tile size versus wasted pixels for a 1024×768 map view;

FIG. 10A is a graph of tile size versus bytes accessed for several different map view sizes;

FIG. 10B is a graph of tile size versus tiles accessed for several different map views sizes;

FIG. 11A is a table relating tile size to decode time for two commonly used formats;

FIG. 11B is a graph of tile size versus decode time;

FIG. 12A is a schematic block diagram of the system of the present embodiment for converting source image data to tile data;

FIG. 12B is a flowchart of the method of the present embodiment for converting source image data to tile data;

FIGS. 13A-1, 13A-2, 13B-1, 13B-2, 14-1, and 14-2 are exemplary software code and data type definitions for creating a base scale of a tile set and for creating lower resolution scales;

FIG. 15A is a schematic block diagram of the system of the present embodiment for storing image tiles;

FIG. 15B is a flowchart of the method of the present embodiment for storing image tiles;

FIG. 16A is a hierarchical diagram of tiled image layers;

FIG. 16B is a pictorial representation of the world divided into clusters;

FIG. 16C is a hierarchical diagram of a five-level cluster;

FIG. 17A illustrates equations for computing the number of tiles for a tile set with a specific number of layers,

FIG. 17B is a table presenting the structure of the index file and the structure of the time image section;

FIG. 18A is a hierarchical diagram of levels and their associated clusters;

FIG. 18B is the hierarchical diagram of FIG. 18A illustrating in addition storage of the top image

FIG. 19A illustrates the structure of the tiled image file of the present embodiment;

FIG. 19B illustrates the structure of the tile index file and the structure of the row index file of the present embodiment;

FIGS. 20A-1, 20A-2, 20B-1, 20B-2, 20C-1, and 20C-2 are software code listing for tile output code and tile input code;

FIG. 21A is a schematic block diagram of the system of the present embodiment for storing and retrieving tiled image data; and

FIG. 21B is a flowchart of the method of the present embodiment for storing and retrieving tiled image data.

DETAILED DESCRIPTION

The problems set forth above as well as further and other problems are solved by the present teachings. These solutions and other advantages are achieved by the various embodiments of the teachings described herein below.

Referring now to FIG. 2, tile-based mapping systems map positions on the earth 11 to a two-dimensional surface 13 and divide that surface into a series of regularly spaced grids 15. Map tiles are discretely addressed, and a translation method between tile addresses and a continuous geospatial coordinate system is defined. This logical tile scheme forms a multi-resolution, regularly spaced grid that is tied to a single two-dimensional map projection which allows a tiled image to be accessed directly with discrete coordinates. For example, instead of requesting a map image with a bounding rectangle delineated with continuous real numbers like [−100.0, 30.00] to [−80.0, 40.0], a tile can be requested from a grid with zoom level, column, and row addresses delineated with discrete integer values.

Referring now to FIG. 3A, there is a mapping between the address of a tile to the geospatial coordinates for the area covered by the tile. One possible way to do this, for example, is to start with a geodetic projection which portrays the earth as a rectangle 360° wide and 180° tall. In this case, the base projection and the logical tile scheme have 2-to-1 aspect ratios. At zoom level one 17, the logical tile scheme has one row and two columns. Each subsequent zoom level, for example, zoom level two 19, has double the number of rows and columns and four times the number of tiles as the previous zoom level. At each increase in zoom level, each tile is divided into four sub-tiles. Although there is no theoretical maximum number of zoom levels, the practical limit is twenty. The number of columns for a zoom level i is 2^(i) and the number of rows is 2^(i-1). Referring now to FIG. 3B, the tile address can be related to a geographic bounding rectangle as per equations 21 and 23.

Referring now to FIG. 4A, before a tile set can be created from a set of random source images, the base scale or a target base scale can be chosen to substantially match the resolution of the source images because a given set of random source images may not match exactly one of the predetermined scale resolutions. Degrees per pixel (DPP) 25 can be used to choose base scales for sets of source images. Information about the sources images, such as image width and height in pixels, and minimum and maximum vertical and horizontal coordinates in degree, are used in the present embodiment to convert the source image to a tile set. DPP 25 can be computed by combining the vertical and horizontal dimensions of the image when tiled image projections preserve the same DPP in each dimension as the logical tile scheme and when the calculations are performed in degrees. Referring now to FIG. 4B, zoom levels (scales) 309 in an example logical tile scheme with 512×512 pixel tiles are shown. Source images stored in other projections might use meters for the coordinate system, requiring a conversion to degrees. For example, is a set of source images has a DPP of 0.03, this falls between scales 4 and 5. If scale 4 is chosen, the sources images will be scaled down and data will be lost. If scale 5 is chosen, the source images will be scaled up, preserving all data, but requiring more storage space. As an example, if the source image set is 10 million bytes uncompressed and has a DPP value of 0.03, when converted to scale 4, the source image will be 4.66 million bytes, and when converted to scale 5 will be 18,645 million bytes. After the tiled images for the base scale have been created, the lower resolution scale tiled images can be created.

When a user moves a map, a tiled mapping client can calculate which tiles are necessary to fill the map, can fetch the tiles, and can stitch the tiles together on the map. A map is defined by both geographic area and pixel area. To calculate which tiles to retrieve, if the client supports only discrete map scales, the client need only know the current zoom level, the tile index of the origin of the map, and the number of tiles required to fill the map. To provide the tiles, however, source images must be converted to tiles, and for this, a determination of the most efficient tile size is needed.

Each raster image is a grid of pixels, and each pixel represents the color of the image at a point in the image. Pixel values are expressed in units of the image's color space, or the abstract model that describes how color components can be represented, e.g. the RGB (red-green-blue) model requires that color components for red, green, and blue be stored as separate values for each pixel. The RGB components are usually stored as single byte values, i.e, integer values from 0 to 255, in a 4-byte integer word. Raster image pixels are addressable using two-dimensional coordinates with an orthogonal coordinate system over the image. Cartesian coordinates can be used for a mapping coordinate system, where the center of the coordinate space is (0,0). Raster images can be stored in formats that can be distinguished by how they handle compression issues, for example, JPEG (lossy compression), PNG (lossless compression), and BMP, PPM, PGM, and PBM (no compression). There are also file formats that have been adapted for storing geospatial images, for example, MrSID (LIZARDTECH®), JPEG2000, and GEOTIFF. Source images can be scaled because tiled images are stored in fixed resolutions that are unlikely to match source image resolutions. Image scaling is a type of interpolation for which there are common algorithms such as, for example, but not limited to, nearest neighbor, bilinear, and bicubic.

Referring now to FIGS. 5 and 6, each image has overhead including the overhead of multiple seeks and reads from a file system, uneven utilization of the file system's native block size, and the header and other overhead storage space within each image file. Common image formats such as JPEG and PNG contain header information and image metadata, and “wasted pixels” 123 (FIG. 5), pixels that are transmitted but are not part of the map view 43 (FIG. 5). For a particular image size 11 (FIG. 6), JPEG format contains JPEG bytes 33 (FIG. 6) and JPEG overhead percentage 37 (FIG. 6). Likewise, for a particular image size 11, PNG contains PNG bytes 35 (FIG. 6) and PGN overhead percentage 39 (FIG. 6). Clearly, lossy JPEG compression leads to a higher relative overhead than lossless PNG compression. Using images that are large enough to reduce image overhead, but not so large as to consume too much memory, or require too much time to load the image, can provide optimum response time. A goal can be to minimize the number of individual images required to virtualize the map view and at the same time minimize the number of wasted pixels 123 (FIG. 5).

Referring now primarily to FIG. 7A, system 100 of the present embodiment for determining the tile size for a particular virtualized map view can include, but is not limited to including, map view generator 101 generating a plurality of random map views for a randomly-selected scale, tile calculator 103 calculating a number of tiles needed to fill each of the random map views for a plurality of tile sizes, a total number of tiles accessed 119 (FIG. 9A), and a total number of bytes accessed based on the total number of tiles accessed, to fill each of the random map views for the plurality of tile sizes, and tile size selector 105 selecting an optimum tile size based on minimizing the total number of bytes accessed for the tile size. Tile size selector 105 can optionally minimize a decompression time based on an image format associated with the each of the random map views. Optionally, system 100 can include, but is not limited to including, pixel scalar 107 scaling pixels in each of the tiles to match the randomly selected scale, calculating a wasted pixel number 123 (FIG. 9A) of scaled pixels from the tiles that are partially outside the random map views for each of a plurality of preselected tile sizes, and selecting the optimum tile size based on minimizing the wasted pixel number 123. Map view generator 101 can include, but is not limited to including, center generator 109 generating random center locations, and for each of the plurality of tile sizes, generating a map view by starting at a center location and extrapolating to a 2-d map view. Center generator 109 can further optionally select the center locations from −180 to +180 longitude and −90 to +90 latitude. Tile calculator 103 can include, but is not limited to including, wasted tile calculator computing wasted tiles as the tiles beyond earth boundaries of the random map views, and computing the total number of tiles accessed based on the wasted tiles.

Referring now primarily to FIG. 7B, method 150 of the present embodiment for determining the tile size for a particular virtualized map view can include, but is not limited to including, the steps of generating 151 a plurality of random map views for a randomly-selected scale, calculating 153 a number of tiles needed to fill each of the random map views for a plurality of tile sizes, calculating 155 a total number of tiles accessed 119 (FIG. 9A), and a total number of bytes accessed based on the total number of tiles accessed, to fill each of the random map views for the plurality of tile sizes, and selecting 157 an optimum tile size based on minimizing the total number of bytes accessed for the tile size. The step of selecting an optimum tile size can include, but is not limited to including, the step of minimizing a decompression time based on an image format associated with the each of the random map views. Optionally, method 150 can include, but is not limited to including, the steps of scaling pixels in each of the tiles to match the randomly selected scale, calculating a wasted pixel number 123 (FIG. 9A) of scaled pixels from the tiles that are partially outside the random map views for each of a plurality of preselected tile sizes, and selecting the optimum tile size based on minimizing wasted pixel number 123 (FIG. 9A). The step of generating a plurality of random map views can include, but is not limited to including, the step of generating random center locations, and for each of the plurality of tile sizes, generating a map view by starting at a center location and extrapolating to a 2-d map view. Method 150 can further optionally include the step of selecting the center locations from −180° to +180° longitude and −90° to +90° latitude. The step of calculating a total number of tiles accessed can include, but is not limited to including, the steps of computing wasted tiles 123 (FIG. 9A) as the tiles beyond earth boundaries of the random map views, and computing the total number of tiles accessed 119 (FIG. 9A) based on the wasted tiles.

For example, for a map scale defined as having 2¹⁰ (1024) columns by 2⁹ (512) rows, each tile is 1024/360:0 (2:84) degrees wide and long. Since all map views have the same aspect ratio, to generate random map views, a number of random center locations can be generated. For each tile size, the map view bounds can be extrapolated from the center location. In some cases, a portion of the map view might go beyond the normal bounds of the earth, for example, the longitude might be greater than 180° or less than −180°. In these cases, the randomization function can be constrained, or wasted pixels and tiles 123 can be computed as if they were legitimate pixels and tiles. in the latter case, the “wasted pixels” 123 can be used to perform wrapping in the boundary areas.

Referring now primarily to FIG. 8A, random map center algorithm 45 can generate 10,000 randomized map center locations for scale 10 and tile dimensions of 16, 32, 64, 128, 256, 512, 1024, and 2048. Random map center algorithm 45 can compute the total number of tiles accessed 119 (FIG. 9A) and the wasted pixels 123 (FIG. 9A) for each access. Referring now to FIG. 8B, random map view generator algorithm 47 is an example of how to randomly generate full map views by choosing a single x,y point and extrapolating to a two dimensional map view. Referring now to FIG. 9A, results are shown in the form of tiles accessed 119 and wasted pixels 123 for a 1024×768 map view in which 10,000 random map views are averaged, for various tile sizes 49. Referring now to FIG. 9B, tile size versus tiles accessed graph 55 of the normalized number of tiles accessed 119 (FIG. 9A) and of pixels wasted 123 (FIG. 9A) is shown. As shown, 16×16 tiles require the most bytes to be read, but generate relatively few wasted pixels 123. Tile sizes 128, 256, and 512 are closest to optimum tile size 125 (FIG. 7A) for this example.

Referring now primarily to FIG. 10A, tile size versus bytes accessed 121 (FIG. 7A) graph 57 for map resolutions 640×480, 800×600, 1024×768, 1280×960, 1400×1050, and 1600×1200 are shown. As shown, optimum tile sizes 125 (FIG. 7A) are 128, 256, and 512. Referring to FIG. 10B, JPEG bytes accessed versus differences from one tile size to another graph 59 is shown. The substantially flat line between tile size 256 and the size 512 indicates that there is little difference between the total bytes accessed for tile sizes 256 and 512.

Referring now to FIG. 11A, decode time table 61 presents the computation time required to decompress compress tiles images is shown as average decode times for tiles of varied sizes in both JPEG and PING formats, and shown in FIG. 11B, tile size versus total decode time graph 63 shows a variety of map resolutions as above. The minimum computation time is shown to be for tile size 512. If, in these examples, the fixed map scale is replaced with a randomly selected map scale chosen from a continuous range instead of fixed discrete scales, the pixels can be scaled to match the scale of the map view with the randomly chosen scale.

Pull-based and push-based are iteration schemes available for creating tiles from random source images. In pull-based tile creation, tiles are iterated over and source image data are pulled from source images for each tile. In push-based tile creation, source images are iterated over and source image data are pushed from each source image to image tiles. To reduce the amount of memory needed for creating tiles, the pull-based scheme with a memory cache of source images can be used. In particular, in the present embodiment, a least recently used (LRU) cache of decoded source images is constructed in memory. If an element is added to an already-full cache, the least recently used element will be discarded. Each time a source image is accessed, the system of the present embodiment checks the LRU cache first for the source image, and only if the source image is not in the LRU cache is it read, decoded, and placed in the LRU cache. Tiles can be iterated over in geographic order. Since source images affect groups of tiles that border each other geographically, a substantial percentage of the source image accesses could be from the LRU cache.

Referring now to FIG. 12A, system 200 for converting source image data to tile data can include, but is not limited to including, image set selector 201 selecting at least one source image set 217, scaling value processor 203 computing a scaling value 219 for the at least one source image set 217, base scale selector 205 selecting a base scale 221 for a tile set to be created based on scaling value 219, geographic bounds processor 207 establishing tile set geographic bounds 223 of the tile set, tile set converter 209 converting tile set geographic bounds 223, and source image processor 211 performing the following steps for each source image 225 from each of the at least one source image sets 217: (i) determining source image geographic bounds 227 of source image 225, (ii) if there is an intersection between the source image geographic bounds 227 and tile set geographic bounds 223, (1) loading source image 225 from a LRU cache, if possible, (2) if source image 225 is not in the LRU cache, loading source image 225 into the LRU cache, (3) extracting image data from source image 225 at the intersection, (4) scaling the image data based on base scale 221, (5) storing scaled image data 229 to tile storage mechanism 231. System 200 also includes cache processor clearing the LRU cache, and loop processor 215 activating each element of system 200 for each of the at least one source image sets 217. Base scale selector 205 can choose base scale 221 to substantially match the resolution of source IMAGE 225. System 200 can optionally include a source image accessor accessing an image width in pixels of source image 225, an image height in pixels of source image 225, and the minimum and maximum vertical and horizontal coordinates in degrees of source image 225. Tile set geographic bounds 223 can be based on source image geographic bounds 227. System 200 can optionally include a memory cache caching tile sets in memory to improve performance. Source image accessor 217 can partially read source images 225. System 200 can optionally include a tile creation algorithm processor multi-threading the tile creation algorithms and using tile creation algorithms for distributed computing. System 200 can optionally include a partial update processor partially updating existing tiled image sets.

Referring now to FIG. 12B, method 250 for converting source image data to tile data can include, but is not limited to including, the steps of (a) selecting 251 at least one source image set, (b) computing 253 a scaling value for the at least one source image set, (c) selecting 255 abuse scale for utile set to be created based on the scaling value, (d) establishing 257 the tile set geographic bounds of the tile set, (e) converting 259 the tile set geographic bounds, (f) for each 261 source image from each of the at least one source image sets (i) determining source image geographic bounds of the source image, (ii) if there is an intersection between the source image geographic bounds and the tile set geographic bounds, (1) loading the source image from a LRU cache, if possible, (2) if the source image is not in the LRU cache, loading the source image into the LRU cache, (3) extracting image data from the source image at the intersection, (4) scaling the image data based on the base scale, (5) storing the scaled image data to a tile storage mechanism, (g) clearing 263 the IA cache, and (h) repeating 265 steps (a) through (g) for each of the at least one source image sets. The step of selecting abuse scale can include, but is not limited to including, the step of choosing the base scale to substantially match the resolution of the source data. Method 250 can further include the steps of accessing an image width in pixels of the source image, an image height in pixels of the source image, and the minimum and maximum vertical and horizontal coordinates in degrees of the source image. The tile set geographic bounds can be based on the source image geographic bounds. Method 250 can include, but is not limited to including, the steps of caching tile sets in memory to improve performance, partially reading the source images, multi-threading the tile creation algorithms, using tile creation algorithms for distributed computing, and partially updating existing tiled image sets.

Referring now to FIGS. 13A-1, 13A-2, 13B-1, 13B-2, 14-1, and 14-2, exemplary and data type definitions 65 and tile set creation code 67 and lower resolution scales creation code 69 for executing the steps of method 250 (FIG. 13B) are shown. TileAddress.getBoundingBox( ) provides the bounding coordinates in degrees for an image tile address. “BoundingBox.intersects( ) tests if two bounding boxes intersect each other. BoundingBox.union( ) is used to combine multiple bounding boxes into a single one. The abstract method writeTile is used to provide a generic means for storing tiles. Additional abstract methods getSourceImageData and putSourceImageData are used to provide access to the LRU source image cache. The constant TILE_SIZE represents the width and height of the tiled images, and is the name for the horizontal and vertical dimensions. Exemplary tile set creation Java code 67 is shown for creating a base scale of a tile set (single-threaded) (FIG. 13A) and exemplary lower resolution scales creation Java code 69 (FIG. 14). Lower resolution scales can be constructed directly and exactly from four tiles from the previous scale as follows. For each scale from a based scale −1 to 1, (1) determine the bounds of the current tile scale in tile coordinates, (2) initialize the tile storage mechanism, (3) iterate over the tile set coordinates, i.e. for each tile (a) determine the four tiles from the higher scale that contribute to the current tile, (b) retrieve the four tile images, or as many as exist, (c) combine the four tile images into a single, scaled-down image, (d) save the completed tiled image to the tile storage mechanism, and (e) finalize the tile storage mechanism. To implement the previous set of steps, the types defined in the previous section can be used, as well as abstract class TileInputStream {abstract BufferedImage getTile{TileAddress address};} This type can allow reading of the tiles from previous scales, assuming that TileInputStream and TileOutputStream are linked somehow to allow writing tiles in one stage and reading them in another stage. For example, when creating scale 7, scale 7 tiles can be written to TileOutputStream, and then read when scale 6 is created.

Because reading from and writing to disk can be time-consuming steps in the tile creation process, following are optional optimizations that can minimize both of these. For example, if there is enough memory to store a significant subset of the tiled images, the source images can be looped through, read only once each, and the data from the source images can be applied to the tiled images. When all source images have been read, the tiled images can be stored in memory so that they may be accessed when creating the lower resolution scales. If there is not enough memory to hold the complete tile set uncompressed, the tile sets can be subdivided into, for example, but not limited to, geographic areas. Memory-based tile creation can include, but is not limited to including, the steps of (1) choosing a base scale for the tile set, (2) deterring the geographic bounds of the tile set (this can be based on the bounds of the source images), (3) determining the bounds of the tile set in tile coordinates, (4) initializing the tile cache, (5) iterating over the source images, for each source image (a) computing the bounds of the source image in tile coordinates, (b) reading the source image into memory, (c) iterating over the tile set coordinates, for each tile (i) computing the geographic bounds of the tile, (ii) checking the cache for the tile image, if it is not in the cache, creating an empty image and putting it in the cache, (iii) extracting the required image data from the source image and storing it in the tied image, (6) for each scale from base scale −1 to 1, (a) determining the bounds of the current tile scale in tile coordinates, (b) iterating over the tile set coordinates, for each tile (i) determining the four tiles from the higher scale that contribute to the current tile, (ii) retrieving the four tile images from the cache, or as many as exist, and (iii) combining the four tile images into a single, scaled-down image.

To organize blocks of data into scales, rows, and columns so that tiled images can be efficiently written to and read from disk, data are divided into clusters in which there are a fixed number of tiles. The clusters, in turn, are divided into multiple levels. Tiles are stored sequentially in a single file, but not in any particular order because they are indexed. The cluster in which a given tile should be placed can then be determined.

Referring now to FIG. 15A, system 300 for storing a dataset of image tiles can include, but is not limited to including, zoom level processor 301 determining a number of zoom levels 309, cluster file processor 303 accessing a plurality of cluster files 313 including two top cluster files, the two top cluster files including a first subset of the zoom levels 309, image tile processor 305 accessing image tiles 317, each image tile 317 having a tile zoom level and a tile location. For each image tile 317, image tile processor 305 computes a cluster name 319 based on tile zoom level 309 and the tile location. For each image tile 317, if a selected cluster file 313 from the plurality of cluster files has a name that matches the computed cluster name, tile pointer processor 307 computes an image tile pointer for the image tile associated with the computed cluster name, stores the image tile pointer in a fixed length index in the selected cluster file, and stores the image tile associated with the computed cluster name in the selected cluster file according to the image tile pointer. For each of the image tiles, if a selected cluster file from the plurality of cluster files has a name that does not match the computed cluster name, zoom level processor 301 determines an other subset of the zoom levels, the other subset not including the zoom levels of the first subset, cluster file processor 303 creates a new cluster file as part of the plurality of cluster files, the new cluster file having a new cluster file index of fixed length, the fixed length based on the other subset of zoom levels, the new cluster file associated with the tile location, tile pointer processor computes an image tile pointer for the image tile associated with the computed cluster name based on the tile zoom level and the tile location, and stores the image tile pointer in the new cluster file index in the new cluster file, and image tile processor 305 stores the image tile associated with the computed cluster name in the new cluster file according to the image tile pointer. Zoom level processor 301 optionally determines a lowest zoom level in the other subset of zoom levels. Image tile processor 305 optionally copies each of the tile images at the lowest zoom level from each of the new cluster files, and stores each of the copied tiled images into the two top cluster files based on the tile location.

Referring now to FIG. 15B, computer-implemented method 350 for storing a dataset of image tiles can include, but is not limited to including, the steps of (a) determining 351 a number of zoom levels, (b) accessing 353 a plurality of cluster files including two top cluster files, the two top cluster files including a first subset of the zoom levels, (c) accessing 355 the image tiles, each of the image tiles having a tile zoom level and a tile location, (d) for each of the image tiles, computing 357 a cluster name based on the tile zoom level and the location, (e) for each 359 of the image tiles, if a selected cluster file from the plurality of cluster files has a name that matches the computed cluster name, (i) computing an image tile pointer for the image tile associated with the computed cluster name, (ii) storing the image tile pointer in a fixed length index in the selected cluster file, and (iii) storing the image tile associated with the computed cluster name in the selected cluster file according to the image tile pointer, and (f) for each 361 of the image tiles, if a selected cluster file from the plurality of cluster files has a name that does not match the computed cluster name, (i) determining an other subset of the zoom levels, the other subset not including the zoom levels of the first subset, (ii) creating a new cluster file as part of the plurality of cluster files, the new cluster file having a new cluster file index of fixed length, the fixed length based on the other subset of zoom levels, the new cluster file associated with the tile location, (iii) computing an image tile pointer for the image tile associated with the computed cluster name based on the tile zoom level and the tile location, (iv) storing the image tile pointer in the new cluster file index in the new cluster file, and (v) storing the image tile associated with the computed cluster name in the new cluster file according to the image tile pointer. Method 300 can optionally include the steps of determining a lowest zoom level in the other subset of zoom levels, copying each of the tile images at the lowest zoom level from each of the new cluster files, and storing each of the copied tiled images into the two top cluster files based on the tile location.

Referring now to FIG. 16A, tiled image layers follow pyramid type structure 71. Each level has four times the number of tiles as its predecessor. Each lower resolution level is based on the image data from the next higher resolution level. Referring now to FIG. 16B, the cluster grouping system of the present embodiment starts by dividing the world into clusters 73, that is, (0,0), and (0,1). Referring now to FIG. 16C, the structure of five-level cluster 75 is shown. The tiles that fall into the area marked by address (0,0) are stored in cluster (0,0) and all the tiles that fall into the area marked by address (0,1) are stored in cluster (0,1). In this embodiment, no tiles overlap both clusters.

Referring now to FIG. 17A, tile set equation 77 computes the number of tiles for a tile set with L levels, and cluster equation 79 computes the number of tiles for a cluster with L levels. To store tiles in cluster files, the number of levels to be stored is determined. For example, with a base level of seven, two cluster files are needed, each with seven levels of tiles and 5,461 tiles. Because the possible number of tiles is fixed for each cluster, a single fixed length lookup index can be built and stored at the beginning of the cluster file. The index size is the number of possible tiles times the size of the tile address record. After the index, the tile images can be stored sequentially in the file. Because there is an index, there is no need to store the tiles in any particular order. Referring now to FIG. 17B, index section 81 and time image section 83 can be included in a file structure for an exemplary cluster file.

Referring now to FIG. 18A, the present embodiment also accommodates multiple levels of clusters with each level covering a continuous sub-range of levels. For example, a tile set with fifteen scales has two levels of clusters. First level 85 includes tile levels 1-7, while the second level 87 of clusters includes tile levels 8-15. First level 85 includes seven levels, while second level 87 includes eight scales. First level 85 of clusters can only have two clusters, while second level 87 of clusters can include as many clusters as there are tiles in the first the level of the second cluster level, in the previous example, the level eight, or 32,768 clusters. In one embodiment, cluster files are only created when there are tiles that belong in the cluster, so that the actual required number of clusters can fluctuate based on the size of the tile set. Referring now to FIG. 18B, to minimize the number of times a file is opened, closed, and accessed, top level image 89 for a subordinate cluster can be duplicated in the first level cluster.

Referring to FIG. 19A, all tiles for a specific zoom level (see FIG. 3A) can be stored in a single file. For each zoom level, there is tiled image file 421 for the tiled images, and there are tiled index file 95 and row index file 411 into the zoomed image file. System 400 (FIG. 21A) of the present embodiment can store a sentinel value, the tile's address, and the tile's size along with the tiled image data sequentially in tiled image file 421. Referring now to FIG. 19B, the system can store only rows in tiled index file 95 in which there are tiles, and can create row index file 411 having either the location of the row's index records from tiled index file 95 if the row has any tiles, or a null value if the row has no tiles, for each row. To retrieve the address for a specific tile, system 400 (FIG. 21A) can seek to the position of the row pointer in row index file 411, read the value, and use the value to position tiled index file 95 if the value is non-null. Further system 400 can seek additional positions for the column index and reading the tile address. Since the tiles do not have to be stored in any particular order, tiles can be written over a period of time, and new tiles can be added to the file by writing them at the end of the file. Referring now to FIGS. 20A-1, 20A-2, 20B-1, 20B-2, 20C-1, and 20C-2, exemplary tile output code 97 (FIG. 20A-1) and exemplary tile input code 99 (FIG. 20B-2) are the Java code for indexed tile output by zoom level and tile input, respectively.

Referring now to FIG. 21A, system 400 for storing and retrieving tiled image data can include, but is not limited to including, tile record processor 401 executing, for each of a plurality of tiles at a pre-selected zoom level from the tiled image data, the step of storing tile record 403 in tiled image file 421, tile record 403 being associated with row 419 and column 423. System 400 can also include lookup table processor 407 creating lookup table 418 having a direct-lookup value for tile record 403 at row 419 and column 423 associated with the tiled image, when there are no tile records 403 at first row 417 and column 423 of lookup table 418, storing a null value in lookup table 418 at row 419 and column 423, when there are no tile records 403 in a lookup table row in lookup table 418, omitting the lookup table row from lookup table 418. System 400 can still further include row index file creator 409 creating row index file 411 having a null value for each of the omitted lookup table rows, and tile retriever 413 retrieving an address for a specific tile by executing the steps including, but not limited to seeking to a row position of row 419 associated with tile record 403 in row index file 411, reading row index value 417 at the position, positioning the tile index file according to the row index value 417 if the value is non-null, seeking to a column position for column 423 associated with tile record 403, reading an address associated with tile record 403, and retrieving tile record 403 at the address. Tile record 403 can include, but is not limited to including, a sentinel value, a tile address, a tile size, and a tiled image. Tile record processor 401 can optionally compute the address based on a column index, a row index, and a number of columns.

Referring now to FIG. 21B, method 450 for storing and retrieving tiled image data can include, but is not limited to including, the steps of for each of a plurality of tiles at a pre-selected zoom level from the tiled image data, storing a tile record in a tiled image file, the tile record being associated with a row and a column, creating a lookup table having a direct-lookup value for the tiled record at the row and the column associated with the tiled image, when there are none of the tile records at the row and the column of the lookup table, storing a null value in the lookup table at the row and the column, when there are none of the tile records in a lookup table row in the lookup table, omit the lookup table row from the lookup table, creating a row index file having a null value for each of the omitted lookup table rows, and retrieving an address for a specific tile by executing the steps including, but not limited to seeking to a row position of the row associated with the tile record in the row index file, reading a row index value at the position, positioning the tile index file according to the row index value if the value is non-null, seeking to a column position for the column associated with the tile record, reading an address associated with the tile record, and retrieving the tile record at the address. The tile record can include, but is not limited to including, a sentinel value, a tile address, a tile size, and a tiled image. Method 450 can optionally include the step of computing the address based on a column index, a row index, and a number of columns.

As described herein, for the fixed length index, the exemplary system can be configured to store the pointer to the tile's file position and the tile's size in the fixed length index. In an alternative exemplary embodiment, this storing feature can be expanded to other fields such as the date the tile was created, a hash or checksum of the tile's contents, and cross-reference info to other images. Putting this information in the index can allow the system to quickly check the status of tiles. For example, a user of the system can quickly retrieve all the tiles created after a certain date, by a very fast lookup in the index. The index lookup can be around 2 orders of magnitude faster than scanning the actual data. Therefore, it would take about 1 second versus 100 seconds to scan a 2 GB tile file. Dates, hashes, or other info that can be represented in a fixed length can all work with this technique. One of ordinary skill in the art will understand that other types of information can also be stored in the index.

In an exemplary embodiment of the invention, a system for hierarchical synchronization of tiles between different computer systems, or datasets, (e.g., a copy of a dataset on a user's computer system and the most recent copy of the dataset on another computer, or central server) is described. The cluster structure described herein is crucial to this system for hierarchical synchronization of tiles. For example, in an image set containing 20,000 clusters, with each cluster containing 2000 tiles, that is 40 million tiles. In a current system, if those 40 million tiles were maintained on a central server and a remote user wants to maintain an exact up-to-date copy of those 40 million tiles, that remote user would have to perform 40 million time checks. Obviously, this would be very difficult without some advanced technique to speed up the process. Accordingly, there is a need in the art for such an advanced technique.

In an exemplary embodiment, a system for hierarchical synchronization of tiles between different datasets can have the clusters keep a composite hash value to solve this issue. Specifically, each tile in a cluster can have a hash value computed. The hash value can be some number of bytes that represents the unique content of the image. In one embodiment, each tile hash value can be 256 bytes. Hash collisions are typically rare enough for this size, that an assumption can be made that each hash is unique; however, one of ordinary skill in the art will understand that different types and sizes of hashes can be utilized.

For a particular cluster, the system can concatenate all the hashes of tiles for that particular cluster together. More specifically, the system can simply take all the hashes from the tiled images of that cluster, and put them into a single long string. Then the system can compute the hash on that single long string, or “composite” hash. This type of method can be called a second order hash. In an exemplary embodiment of the invention, the concatenation step can be performed ahead of time after any changes are made to a cluster and stored in the cluster

The system can then use the composite hash for each cluster, or cluster single hash, to see if the contents of the cluster have changed by quickly comparing clusters. If the system finds that the cluster single hashes don't match, then the system can get all the separate image hashes and start comparing them to see which specific ones don't match.

Returning to the previous example, the remote user can request the cluster single hash for each of the 20,000 clusters in the image set. Typically, this does not take long to return and parse. Then, each cluster's hash can be compared to the corresponding hashes in the user's dataset. Next, only if a particular cluster's hash is different (i.e., has changed) between the datasets, the remote user can request all the hashes of the tiles inside that particular cluster. The system would then return 2000 hashes, for example, inside that cluster, which should, again, not take long to return and parse. Finally, the user can then just pull down the tiles in that particular cluster that have changed, and are needed to be updated on the user's system.

In an alternative exemplary embodiment of the invention, another system for hierarchical synchronization of tiles between different computer systems is described. In this alternative embodiment, the datasets of image tiles are not in clusters. Therefore, the system can take advantage of the fact that lower resolution tiles (e.g., those tiles at the top of the hierarchical pyramid structure) are dependent on the full resolution at the bottom of the hierarchical pyramid structure. If a single tile at the bottom of the hierarchical pyramid structure changes, some part of the top of the hierarchical pyramid structure will also change. This minor change may not be visible to the eye when viewing the top level tile; however, it will show up in the hash of the top level tile's contents.

Accordingly, to perform a remote synchronization in this exemplary embodiment, the system can initially check the top level tile's hash. If the top level tile's hash has changed since the last check, the system can request the next level sub tiles (e.g. 4 sub titles on the second row of the pyramid structure) and check those hashes. The system can perform this recursively by checking tiles and then requesting the next level sub tile hashes until the system gets to the bottom of the pyramid, and finds all the tiles with different hashes. If there are no changes to any tiles in the pyramid structure, then the top tile hash will be the same, and the system would only need 1 query to determine that. Therefore, this embodiment can be very efficient for datasets of tiles that do not change very often.

In an exemplary embodiment, the two alternative methods described can be alternatively employed in a hierarchical synchronization system. Specifically, the system can determine which method to utilize depending on the frequency in which the data is changed. Datasets that frequently change can use the cluster method, and datasets that rarely change use the level has approach. A dynamic heuristic can be designed to automatically determine which method to use.

Embodiments of the present teachings are directed to computer systems for accomplishing the methods discussed in the description herein, and to computer readable media containing programs for accomplishing these methods. The raw data and results can be stored for future retrieval and processing, printed, displayed, transferred to another computer, and/or transferred elsewhere. Communications links can be wired or wireless, for example, using cellular communication systems, military communications systems, and satellite communications systems. In an exemplary embodiment, the software for the system is written in FORTRAN and C. The system operates on a computer having a variable number of CPUs. Other alternative computer platforms can be used. The operating system can be, for example, but is not limited to, WINDOWS® or LINUX®.

The present embodiment is also directed to software for accomplishing the methods discussed herein, and computer readable media storing software for accomplishing these methods. The various modules described herein can be accomplished on the same CPU, or can be accomplished on a different computer. In compliance with the statute, the present embodiment has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the present embodiment is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the present embodiment into effect.

Referring again primarily to FIGS. 7B, 12B, 15B, and 21B, methods 150, 250, 350, and 450 can be, in whole or in part, implemented electronically. Signals representing actions taken by elements of systems 100 (FIG. 7A), 200 (FIG. 12A), 300 (FIG. 15A), and 400 (FIG. 21A) and other disclosed embodiments can travel over at least one live communications network. Control and data information can be electronically executed and stored on at least one computer-readable medium. The system can be implemented to execute on at least one computer node in at least one live communications network. Common forms of at least one computer-readable medium can include, for example, but not be limited to, a floppy disk, a flexible disk, a hard disk, magnetic tape, or any other magnetic medium, a compact disk read only memory or any other optical medium, punched cards, paper tape, or any other physical medium with patterns of holes, a random access memory, a programmable read only memory, and erasable programmable read only memory (EPROM), a Flash EPROM, or any other memory chip or cartridge, or any other medium from which a computer can read. Further, the at least one computer readable medium can contain graphs in any form including, but not limited to, Graphic Interchange Format (GIF), Joint Photographic Experts Group (JPEG), Portable Network Graphics (PNG), Scalable Vector Graphics (SVG), and Tagged Image File Format (TIFF).

The invention has been described with reference to certain embodiments. It will be understood, however, that the invention is not limited to the embodiments discussed above, and that modification and variations are possible within the scope of the appended claims. 

What is claimed is:
 1. A method for hierarchical synchronization of tiles between a first dataset and a second dataset, comprising the steps of: computing and storing a plurality of composite cluster hash values for each of a plurality of clusters in the first dataset and the second dataset; for each of the plurality of composite cluster hash values, comparing a composite cluster hash value of a particular cluster in the first dataset with a composite cluster hash value of a corresponding cluster in the second dataset; when the composite cluster hash values of the corresponding clusters of the first and second datasets do not match, retrieving a plurality of tile hashes corresponding to a plurality of tiles from the non-matching cluster in the first dataset and retrieving a plurality of tile hashes corresponding to a plurality of tiles from the non-matching cluster in the second dataset; and determining the one or more changed tiles between the non-matching cluster in the first data set and the non-matching cluster in the second dataset by comparing the corresponding tile hashes, for each of the plurality of tile hashes.
 2. The method of claim 1, wherein the step of computing and storing a plurality of composite cluster hash values for each of a plurality of clusters in the first and second datasets comprises the step of concatenating a plurality of tile hashes of tiles together in each cluster, and computing a hash on the concatenated tile hashes, which generates the composite cluster hash value for the cluster.
 3. The method of claim 1, further comprising the step of copying the one or more changed tiles from the first dataset to the second dataset to match the first and second datasets.
 4. A method for hierarchical synchronization of tiles between a first dataset and a second dataset, comprising the steps of: comparing a top level hash values for each top level tile of the first dataset and the second dataset; if the top level hash value for each top level tile do not match, comparing the second level hash values for each second level tile of the first dataset and the second dataset; recursively comparing the next level hash values for each corresponding level tiles of the first dataset and the second dataset until the bottom level is reached; and determining one or more changed tiles based on any hash level values that do not match.
 5. The method of claim 4, further comprising the step of copying the one or more changed tiles from the first dataset to the second dataset to match the first and second datasets.
 6. A hierarchical synchronization system, comprising: a cluster hierarchical synchronization module, wherein the cluster hierarchical synchronization module is implemented in a computer system that comprises instructions stored in a machine-readable medium and a processor that executes the instructions; a tile hierarchical synchronization module, wherein the tile hierarchical synchronization module is implemented in a computer system that comprises instructions stored in a machine-readable medium and a processor that executes the instructions; and a dynamic heuristic module configured to automatically determine which of the cluster hierarchical synchronization module or the tile hierarchical synchronization module to utilize to synchronize a first dataset with a second dataset depending on a frequency in which a plurality of tiles in the first dataset change, wherein the dynamic heuristic module is implemented in a computer system that comprises instructions stored in a machine-readable medium and a processor that executes the instructions.
 7. The hierarchical synchronization system of claim 1, wherein the cluster hierarchical synchronization module is configured to perform a hierarchical synchronization of tiles between the first dataset and the second dataset by computing and storing a plurality of composite cluster hash values for each of a plurality of clusters in the first dataset and the second dataset; for each of the plurality of composite cluster hash values, comparing a composite cluster hash value of a particular cluster in the first dataset with a composite cluster hash value of a corresponding cluster in the second dataset; when the composite cluster hash values of the corresponding clusters of the first and second datasets do not match, retrieving a plurality of tile hashes corresponding to a plurality of tiles from the non-matching cluster in the first dataset and retrieving a plurality of tile hashes corresponding to a plurality of tiles from the non-matching cluster in the second dataset; and determining the one or more changed tiles between the non-matching cluster in the first data set and the non-matching cluster in the second dataset by comparing the corresponding tile hashes, for each of the plurality of tile hashes.
 8. The hierarchical synchronization system of claim 1, wherein the tile hierarchical synchronization module is configured to perform a hierarchical synchronization of tiles between the first dataset and the second dataset by comparing a top level hash values for each top level tile of the first dataset and the second dataset; if the top level hash value for each top level tile do not match, comparing the second level hash values for each second level tile of the first dataset and the second dataset; recursively comparing the next level hash values for each corresponding level tiles of the first dataset and the second dataset until the bottom level is reached; and determining one or more changed tiles based on any hash level values that do not match. 